Mitt Romney and Republicans have long assumed Barack Obama simply can’t win reelection, given the state of the economy. Yet Obama is currently winning, anyway. Why? Perhaps the unexpected dynamics driving this race can be summed up in two sentences:

1) More Americans are concluding that for all their disappointment, the economy will improve in an Obama second term; and

2) Romney has failed to persuade people that he would improve the economy any faster than it will improve under Obama.

If this explains why Obama is leading, then the Romney campaign’s big question — “are you better off than you were four years ago?” — simply isn’t the dominant frame voters are adopting to choose the next president. Indeed, there is now a great deal of polling that suggests this to be the case. Taken together, the picture is striking:

* In this week’s Fox News swing state polls, Obama holds an advantage on the question of who would improve the economy and jobs in Ohio (50-43), in Virginia (49-44), and in Florida (49-46).

* In this week’s NYT/CBS/Quinnipiac polls of Wisconsin, Virginia, and Colorado, Obama holds an advantage on the economy in two of the three: Wisconsin (49-46) and Virginia (49-47).

* In this week’s NBC/WSJ national poll, disapproval of Obama on the economy is higher than approval, but he still is ahead on who is better prepared to lead in the next four years, 47-36. The past is not necessarily coloring views of the future. Why?

Because more people are concluding things will improve. Forty-two percent think things will get better in the next year — up six points since August and 15 since July.

* This week’s Associated Press poll has similar findings: 49 percent of Americans say the economy will get better over the next 12 months, versus 39 percent who say it will stay the same or get worse. Remember, big majorities expect Obama to get reelected.

* Obama has pulled into a tie with Romney on the economy in the last eight national polls: Pew, AP, NBC/WSJ, NYT/CBS, Rasmussen, Post/ABC, CNN, and Fox News. That’s after Romney led on the issue in many polls for nearly a year.

Romney’s core argument for months has been: You are not better off than you were four years ago; Obama made the economy worse; I will make it better. It’s hard to square all the above polling with the notion that voters are accepting this frame. People who are disappointed in Obama’s economic performance are still concluding he’d do at least as good a job (in some polls) or a better one (in others) than Romney on the economy in the next four years. The “are you better off” question may not be driving decision-making. Perhaps this is partly why Obama is leading.

As I’ve been saying, Romney’s fundamental theory of the race — that the economy makes Obama an all-but-certain loser, meaning Romney only has to clear a minimum threshold of acceptability to win — may have been flawed. Sean Trende, hardly a liberal, is reaching a similar conclusion. The Romney camp’s latest announcement of a reset, in which he’ll supposedly talk more concretely about how his plans will affect families, suggests at least a rhetorical acknowledgment of this.

No question, the economy is still a major burden for Obama, and he’s still a long way from winning. But right now, Americans just don’t seem to be thinking about it the way Romney needs them to.